1. Field of the Invention
This invention relates generally to light direction control, and more particularly, to techniques for the dynamic control of light propagation direction.
2. The Prior Art
Dynamic control of light beam propagation direction is a fundamental technique in optics. Direct applications include projection displays, entertainment, advertisement, laser printers, laser detection systems, laser scanning, optical communications, laser machining, etc. Electromechanical devices have been the most frequently used light scanners in commercial products. Electromechanical methods use a rotating reflector or a rotating refractor driven by an electromechanical mechanism for changing light direction. The most important limitations of the electromechanical scanner include slow speed, bulky size, and the deficiencies inherent in complex electromechanical mechanisms. These limitations are intrinsic due to the nature of mechanical movement at a macro-dimensional scale.
Piezo-electric devices are able to induce small geometric changes on a sub-millimeter scale. Note that there is a significant difference between the macro-dimensional scale and the sub-millimeter scale. These difference extend beyond merely size; they represent different principles of operation and different methods of fabrication. When an electric signal is appropriately applied on a piezoelectric material, such as PZT (Lead Zirconate Titanite), a small dimensional change is induced. The dimensional change is generally in the range of from 1 micrometer (.mu.m) to 500 .mu.m. Piezoelectric actuators are based on such sub-millimeter scale processes. The most notable features of the sub-millimeter scale devices include high speed, miniature size, and simple device structure.
In the prior art, there are two types of piezoelectric light beam deflectors, the simple type and the mechanically enhanced type. Simple piezoelectric light deflectors can produce a small deflection angle ranging from 0.01.degree. to several degrees. They are essentially piezoelectric light deflectors without enhancement. Since the deflection angles produced by the simple piezoelectric deflectors are too small for many practical applications, U.S. Pat. Nos. 3,981,566 and 4,025,203 and other prior art publications disclose mechanically enhanced piezoelectric mechanisms. Mechanically enhanced devices further extended the deflection angle to as large as about 15.degree.. However, mechanically enhanced devices suffer from reduced speed and very delicate mechanical mechanisms at the macro-dimensional scale. The deficiencies of the mechanically enhanced piezoelectric light deflectors are on par with those of other electromechanical devices, while sacrificing the unique advantages of the simple piezoelectric process. Mechanically enhanced piezoelectric light deflectors have proved incapable of competing with other conventional electromechanical light deflectors for commercial applications.